The present invention concerns an apparatus for preparing a flock-air mixture intended for example for forming an absorbent pad and a method of dispersing lumps in a flock-air mixture.
In the case of machines for producing absorbent pads as for sanitary napkins, panty liners, disposable diapers or the like, the usual practice is for an absorbent pad or flock core to be formed from a hydrophilic flock mixture on a flock-laying device. The flocks which are required for that purpose are fed to the flock-laying device in the form of a flock-air mixture, being supplied thereto from a disintegrating or pulping device, through a feed conduit.
For reasons relating to environmental protection and anti-noise measures, it has become the usual practice for the disintegrating device to be arranged spatially separately from the flock-laying device, with a blower or fan being integrated into the feed conduit in order to ensure that the flock-air mixture can suitably cover the conveying distance which has been increased as a result. Due to friction in the feed conduit, flow turbulence phenomena and a static charging effect, flock lumps or compacted pieces of flock are formed within the flock-air mixture as it flows through the greater length of the feed conduit. That contributes to preventing the desired homogeneous flock structure of the absorbent pad and in addition has an adverse effect on the mechanical stability of the absorbent pad as lumps are only laid into the flock mesh structure of the absorbent pad but are not properly bound thereinto.
An additional driven grinding rotor can be integrated into the feed conduit which carries the flock to the flock-laying device, in order to break up the flock lumps, near the flock-laying device. That technology is described for example in U.S. Pat. Nos. 1,834,309, 2,940,133, 2,940,134, 2,940,135, 3,886,629 and 4,375,447. A disadvantage with those known arrangements is that they are generally expensive and they also take up a considerable amount of space. The grinding rotors for disintegrating the flock lumps require a rotary drive, the speed of rotation of which has to be suitably adapted in dependence on the through-put rate of the flock-air mixture. In addition, the rotors give rise to unwanted air turbulence phenomena which act in opposition to the uniform formation of the absorbent pad.
As an alternative to the provision of a grinding rotor in the feed conduit which carries the flock-air mixture, EP 0 515 939 A1 provides for the incorporation of a mechanical impact device in the feed conduit. That impact device comprises a plurality of impact bars which project into the cross-section of the feed conduit for transporting the flock-air mixture. The flock lumps which are contained in the flock-air mixture and which, upon being transported from the disintegrating device to the flock-laying device, impact against the impact bars are very substantially broken up by virtue of that mechanical collision effect. It has been found however that this impact device suffers from the disadvantage that on the one hand considerable amounts of lumps of flock still do not collide with the impact bars and are therefore not broken up, while on the other hand the degree of efficiency in terms of flock lump dispersion depends on the through-put of the flock-air mixture through the feed conduit as it is the through-put speed of the mixture through the feed conduit that determines the speed at which the lumps of flock impact against the bars.
An object of the present invention is to provide an apparatus for preparing a flock-air mixture which is substantially free of flock lumps, which affords an enhanced level of efficiency in terms of dispersing the lumps.
Another object of the invention is to provide an apparatus for preparing a substantially lump-free flock-air mixture, with which the efficiency of lump dispersion is at least substantially independent of the speed of flow of the flock-air mixture through a feed conduit leading to a flock-processing device.
Still another object of the present invention is to provide a method of dispersing lumps of flock in a flowing flock-air mixture, such as to enhance the efficiency with which the lumps are dispersed without substantial dependence on the speed of flow of the flock-air mixture.
Yet another object of the present invention is to provide a method of dispersing flock lumps in a flock-air mixture, which affords a simple but reliable and effective operating procedure.
In accordance with the principles of the present invention, in regard to the apparatus, the foregoing and other objects are attained by an apparatus for providing a flock-air mixture which is to be fed through a feed conduit to a flock-laying device for forming an absorbent pad. Provided in the feed conduit is a dispersing device for dispersing flock lumps within the flock-air mixture. The dispersing device is a pneumatic dispersing device operable to loosen up and disperse flock lumps by accelerating the flock-air mixture together with the lumps contained therein to cause the lumps to be broken up, as by tearing the lumps apart or by causing them to burst asunder.
Further in accordance with the principles of the present invention, in regard to the method aspect, the foregoing and other objects are attained by a method of dispersing flock lumps within a flock-air mixture passing through a feed conduit to a flock-laying device for forming an absorbent pad, wherein, prior to formation of the absorbent pad in the flock-laying device, the flock-air mixture together with the flock lumps contained therein is accelerated by means of a pneumatic dispersing action thereby to cause the flock lumps to break up.
It was surprisingly found that flock lumps which comprise compacted cellulose flocks or fibers can be broken up and dispersed if they are accelerated suddenly with a jerk, jolt or jump by means of a directed flow of fluid, in particular an air flow, of high kinetic energy. In that situation, acceleration and/or fluid friction forces occur, which readily overcome the mechanical and/or electrostatic adhesion forces which are operative between the flocks forming a flock lump. Furthermore, the pneumatic dispersing device according to the invention preferably generates turbulent flows whose acceleration effects which change randomly in respect of direction and magnitude have the result that the flock lumps disintegrate.
Depending on the respective magnitude of the forces which hold a flock lump together, dispersion of the flock lump occurs at an earlier or later time. A flock lump which is less firmly held together can already be torn apart at the beginning of the acceleration phase whereas a flock lump which is more firmly held together can under some circumstances be destroyed only after the attainment of an adequate degree of turbulence in the flow of the flock-air mixture. At any event the apparatus and the method according to the invention provide that, in contrast to the impact arrangements discussed above, all flock lumps contained in the flock-air mixture flowing through the feed conduit are operatively engaged by the acceleration forces to cause appropriate disintegration and dispersion thereof.
In accordance with a preferred feature of the apparatus of the invention, the pneumatic dispersing device can be arranged in the end region of the feed conduit which carries the flow of the flock-air mixture. Preferably, the dispersing device is fitted directly into the opening of the feed conduit into the flock-laying device. The flock-laying device includes a rotating flock-shaping wheel and a stationary flock box into which the feed conduit opens by way of the pneumatic dispersing device. The directed jet of the substantially lump-free flock-air mixture which is produced by the pneumatic dispersing device means that it is advantageously possible for that jet to be directed specifically and targetedly in a given direction in space. This means that troughs or shaping recesses provided in the peripheral surface of the flock-shaping wheel, for forming the absorbent pads, can be more effectively filled with flock.
In accordance with another preferred feature of the invention the pneumatic dispersing device can be formed by a nozzle around which the flock-air mixture flows. The nozzle is arranged substantially in the central region of the cross-section of the feed conduit between the disintegrating device and the flock-laying device. With this configuration of the dispersing device it will be noted that it is necessary for the compressed air which is to be discharged from the nozzle under high pressure to be introduced into the central region of the cross-section of the feed conduit. The consequence of this is that at least one suitable pneumatic line must be passed into the central region of the cross-section of the feed conduit, which means that the at least one pneumatic line is in the flow path of the flock-air mixture and thus, in addition to the pneumatic action of dispersing the flock lumps, can also afford a mechanical dispersing action in the manner of the abovediscussed impact bars.
In a further preferred feature the pneumatic dispersing device is in the form of an injector nozzle in the form of a tube portion, with the flock-air mixture flowing through the injector nozzle itself. A pressure fluid under high pressure, more particularly for example compressed air, is fed to the injector nozzle by way of one and preferably a plurality of flow openings which are in the form of feed passages. The pressure fluid can either come from a pressure fluid source which is additionally provided for that purpose, or it can come from a pressure fluid source which in any case is already present for other systems of the machines involved in the present context. The preferably plurality of feed passages in accordance with the invention can be disposed in the outer peripheral region of the flow space of the injector nozzle, through which the flock-air mixture flows.
It will be appreciated that the pneumatic dispersing device or injector nozzle acts in a fluid-mechanics fashion like a fluid or air flow booster. A reduced pressure obtains at the entry or intake side while an increased pressure occurs at the exit or ejection side thereof. The dispersing device or injector nozzle can therefore act like a suction blower arranged at the end of the feed conduit which carries the flock-air mixture, so that, depending on the respective overall length of the feed conduit, it is possible to forego the inclusion of a further fan or blower in the flock-delivery path.
In regard to a preferred feature of the method of the invention, it has proven to be particularly advantageous for the flock-air mixture to be accelerated to a supersonic speed, preferably to twice the speed of sound. Such high speeds ensure that turbulent flows are produced in the dispersing device or injector nozzle and the flock-air mixture is accordingly sufficiently accelerated with a jerk, jolt or jump effect.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of a preferred embodiment of the invention.